This invention pertains to power transmission, and more particularly to apparatus for driving mobile storage carriages.
Mobile storage systems, for storing books, supplies, and files are in widespread use where it is important to provide high density storage, such as in offices, schools, and libraries. My U.S. Pat. No. 5,007,351 describes an improved power transmission mechanism for use in such systems.
Typical mobile storage systems include two or more parallel rails embedded in or attached to a building floor. One or more relatively long and narrow carriages span the rails. The carriages may exceed eighty feet in length, and the number and spacing of the rails are chosen to suit the particular carriage length. The carriages are usually supported by a pair of wheels rolling along each of the rails.
The carriages may be designed to move along the rails under manual power. For that purpose, a hand wheel is usually mounted to a carriage end panel. The hand wheel is connected by various drive components to a shaft that in turn is connected with at least one of the carriage wheels. Manually rotating the hand wheel causes the drive wheels to rotate and move the carriage. Electrically powered carriages are also in wide-spread use. With that design, a suitable electric motor is substituted for the manual hand wheel. The motor shaft is mechanically connected through a suitable mechanism to the carriage drive wheels.
It has been a common practice to design mobile carriages such that drive wheels are located along the length of the carriage on one side of the carriage. These prior designs require a long shaft for connecting the drive wheels along the carriage length. The long shafts are awkward to assemble and service. In addition, the long shafts generally undergo torsional wind-up when used with heavy carriages, such that, due to twisting of the shaft along its length, the drive wheels at the carriage end remote from the electric motor or hand wheel do not rotate as fast as the drive wheels at the end at which the shaft is rotationally driven. Consequently, despite the use of flanges on the drive wheels, the carriages can tend to skew as they are driven along the rails.
In accordance with my earlier patent, a single driving mechanism was provided at the center of the carriage. However, a need has continued to exist for improved mobile storage carriages with more than one drive mechanism, but which would overcome the aforementioned skewing problem encountered with the prior art.
In accordance with the present invention, drive systems are provided which improve the performance of mobile storage system carriages and which obviate the aforementioned skewing problem.
In accordance with the invention, at least two synchronized transversely spaced drive units each engage separate rails. A single power source such as an electric motor is connected to a drive shaft that spans all of the rails on which drive units are provided. The shaft is provided with drive sprockets which are intermeshed with driven gears of the drive mechanisms. Torsional twisting of the drive shaft is minimized by use of gear ratios between these gears which provide a sufficient mechanical advantage to effectively reduce the torque applied to the drive shaft.
As in the case of my earlier invention, the drive wheels may have central flanges that fit within and are guided by a longitudinal groove in the rail top surface. Alternatively, the wheels may be flat or may be provided with flanges on each side and are adapted to travel on a flat rail. Anti-tip restraining clips may be provided to insure stability of the mobile storage system.
To drive the carriage drive wheels of each drive unit in synchronization, sprockets are provided to which power is transferred by means of a chain trained around the sprockets. The chain is driven by a drive sprocket that is attached to the drive shaft, which is in turn rotated by a power source such as an electric motor or the output shaft of a speed reducer. To provide tension adjustment to the drive chain, the drive sprocket or a separate idler sprocket is preferably made adjustable. The drive units of the present invention may also be driven by manually powered mechanisms.
Briefly, a mobile carriage system of this invention includes a pair of spaced, parallel end rails fixed to a support surface, and, usually, dependent on the length of the carriage, at least one or more intermediate rails fixed to the support surface and located parallel to and between the pair of end rails. At least one carriage is supported for movement on the end and any intermediate rails. The carriage includes an elongated frame that spans all of the rails. At least two drive units, each including a pair of wheels and supporting the carriage on a different one of the rails are provided. The drive units are operatively connected to a drive shaft which extends across a plurality of the rails. The drive shaft and each of the drive units are coupled by a drive gear on the shaft which has a first effective diameter and a driven gear on the drive unit, which has a second effective diameter substantially greater than the first effective diameter. Thus, the drive units minimize torsional twisting of the drive shaft during use. A source of rotational power such as an electric motor is operatively connected to the drive shaft.
Other features of the present invention will become apparent from the claims, detailed description and accompanying drawings.